LED replacement for low voltage lamps

ABSTRACT

The LED replacement for low voltage lamps has a plurality of LED lights disposed in a housing capped by a multifaceted reflector to provide lighting having comparable lighting characteristics to non-LED sourced low voltage lamps. Power conditioning solid state circuitry is disposed in the housing and provides the LED lights with a regulated excitation voltage source. The power conditioning circuitry has at least one ceramic capacitor in parallel with output leads of a power supply for the lamp. A zener diode pair having anodes connected together is disposed in parallel with the ceramic capacitor. The power conditioning circuitry is disposed in advance of a voltage rectifier and filter bank, whose output is provided to a voltage regulator that provides regulated DC voltage to the LED light sources. Output of the voltage regulator is modulated by thermal protection circuitry that throttles the LEDs off responsive to lamp overheating.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/154,000, filed May 28, 2008 now U.S. Pat. No. 7,812,550.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to electrical appliances, and morespecifically to an LED replacement for low voltage lamps that canfunction as a replacement for a low voltage lamp, such as an MR16halogen lamp.

2. Description of the Related Art

“MR” stands for multifaceted reflector, a pressed glass reflector withthe inside (reflecting side) surface composed of facets and covered by areflective coating. The facets provide optical control by gathering thelight from the filament to create a concentrated beam of light. Thereflectors of some MR lamps have a smooth inside surface instead offacets however they are typically still called MR lamps. The typical MRlamp has a single-ended quartz halogen filament capsular light sourcethat is typically powered by a transformerless, electronic power supply.The electronic power supply should be designed to accommodate typicalMR-16 lamp power ratings, which may range from 10 to 100 watts,depending on the lighting application. MR-16 lamps are generallyoperated using voltages lower than 120 volts, nominally 12 volts.However, it is not uncommon to find an MR-16 lamp having an operationalvoltage of 6 or 24 volts. A switching power supply is needed to reducethe line voltage from 120 or 240 volts to the appropriate level forthese lamps. Most MR-16 low-voltage lamps are equipped with a basehaving two electrical contact pins. However, other bases, such as thebayonet style or turn and lock style, may be utilized.

Typically low voltage lighting utilizes a step down magnetic transformerthat operates on 120 volts AC and produces an output of approximately 12volts AC at approximately 60 Hz. This frequency allows the LEDs tooperate without causing a visible flicker in their output. However, inthe event that a transformerless switching power supply is used,problems arise, in that an electronic transformer generally has anoscillator that requires a load in the output before it will switch onand produce current to the output. This load varies with the design ofthe electronic transformer, but is typically set at 8-10 watts. If thetransformer does not sense the load to be at this level, the transformerwill fail to start. Typically, LED-based replacement light sourcespresent a load to the transformer that is ten percent of the transformerrating, which is below the transformer “ON” set point. Moreover, theoutput frequency that the switching power supply oscillator is set tomay be many times higher than the standard 60 Hz line frequency that amagnetic transformer provides. The frequency is high enough that itproduces harmonics in the drive circuitry of the LED light source. SinceLEDs have an 8-10 nanosecond rise time, these harmonics are ofsufficient amplitude to effectively turn the LEDs on and off at afrequency that is a subharmonic of the oscillator frequency, therebycausing the LED source to flicker at a rate that becomes obvious to aperson viewing the light.

Attempts have been made to replace the halogen light source of MR-16 andother low voltage lamps with an LED (light emitting diode) light source.The aforementioned common problem encountered when an LED light sourceis utilized is that the LED's do not draw enough current to activate theswitching power supply. Also switching power supplies may from time totime output transient spikes of voltage that may damage the delicate LEDsources in an LED replacement lamp.

Thus, an LED replacement for low voltage lamps solving theaforementioned problems is desired.

SUMMARY OF THE INVENTION

The LED replacement for low voltage lamps provides a light emittingdiode (LED) replacement for the typical low voltage lamp with a halogenor other non-LED light source. The LED replacement for low voltage lampshas a typical low voltage form factor that comprises a plurality of LEDlights disposed in a housing capped by a multifaceted reflector toprovide lighting having comparable lighting characteristics to thenon-LED sourced low voltage lamps. Power conditioning solid-statecircuitry is disposed in the housing and provides the LED lights with aregulated excitation voltage source. The power conditioning circuitry iscomprised of at least one ceramic capacitor in parallel with outputleads of a power supply for the lamp. Preferably a pair of zener diodeshaving their anodes connected together is disposed in parallel with theceramic power conditioning capacitor. The power conditioning circuitryis disposed in advance of a voltage rectifier and filter bank, whoseoutput is provided to a voltage regulator that provides regulated DCvoltage to the LED light sources. Output of the voltage regulator may bemodulated by thermal protection circuitry that throttles the LEDs dimmeror off, depending on temperature inside the lamp housing.

These and other features of the present invention will become readilyapparent upon further review of the following specification anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an LED replacement for low voltage lampsaccording to the present invention.

FIG. 2 is a plan view of a LED replacement for low voltage lampsaccording to the present invention.

FIG. 3 is a schematic diagram of a first embodiment of driver circuitryfor an LED replacement for low voltage lamps according to the presentinvention.

FIG. 4 is a schematic diagram of a second embodiment of driver circuitryfor an LED replacement for low voltage lamps according to the presentinvention.

FIG. 5 is a schematic diagram of a third embodiment of driver circuitryfor an LED replacement for low voltage lamps according to the presentinvention that provides for dimmer compensation.

Similar reference characters denote corresponding features consistentlythroughout the attached drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIGS. 1-4, the present invention provides an LED replacementfor low voltage lamps. The LED replacement for halogen reflectorreplacement 10 has a typical low voltage bulb form factor that comprisesa plurality of LED lights 15 disposed in a housing 20 capped by amultifaceted reflector 25 to provide lighting having comparable lightingcharacteristics to the halogen sourced lamps. The LED replacement 10 hasa base 30 from which two electrical contact prongs 35 extend.

Power conditioning solid state circuitry 305 and power regulationcircuitry 310 are disposed in the housing and provide the LED lightswith a regulated excitation voltage source. The power conditioningcircuitry 305 is comprised of at least one ceramic capacitor C5 inparallel with output leads J1 and J2 of an exemplary 12-volt AC powersupply for the replacement 10. C5 is preferably ceramic in order toprovide a Mean Time Between Failure (MTBF) of the same order ofmagnitude as MTBF (approximately 50,000+ hours) for typical LED bulbsLED1-LED3. A preferable range of values for capacitor C5 is between0.015 uF at approximately a 50-volt rating. As shown in FIG. 4, analternative embodiment provides a pair of zener diodes U3′ and U4′having their anodes connected together and disposed in parallel with aceramic power conditioning capacitor C13′. Preferably the zener clippingvoltage is set to approximately 19 volts. A preferable range of valuesfor capacitor C13′ is between 0.015 uF at approximately a 50-voltrating.

Referring to FIG. 3, the power conditioning circuitry may include apreferably full-wave voltage rectifier comprised of diodes D1, D2, D3,and D4, the voltage rectifier being connected to a filter bank comprisedof capacitors C1 and C2, which smooth the DC voltage output provided tovoltage regulating LED driver circuitry U1, which, in turn, energizes DCLED light sources 15 (LED1 LED2 and LED3). An exemplary driver U1 may bea Maxim MAX 16820 that provides approximately 2 MHz high-brightness LEDdrivers having high-side current sense and approximately 5000:1 dimming.YIN of the rectifier output is connected to the IN terminal (pin 1) ofdriver U1. Preferably driver U1 can provide an approximately 5-voltregulated output for VIN input voltages ranging from approximately 4.5to approximately 28 volts.

The output of voltage regulating LED driver circuitry U1 may bemodulated by thermal protection circuitry (R3 is a positive temperaturecoefficient thermistor and is in a series divider circuit with resistorR4), which throttles charge to capacitor C4 at dimming input DIM (pin 3)of U1 to the LEDs, LED 1, LED 2, and LED 3, via shunt regulator U2 togradually dim and turn off the LEDs when temperature inside the lamphousing 20 exceeds a predetermined safe threshold temperature.Preferably the power throttling back is set to begin at approximately60° C. and the throttling back gradient is set to cut the power by 50%at approximately 73° C. (or 85% of the maximum allowable temperature) toprevent thermal damage of the lamp system 10 due to unforeseenconditions. The power may be throttled back by either pulse widthmodulation (PWM) means or linear means. Set point of U2 is determined byresistors R5 and R6 in relation to thermistor R3 and R4.

Forward bias of shunt regulator U2 is provided by the series combinationof resistors R1 and R2, R1 being directly connected to the plus side VINof the filtered DC voltage. Shunt regulator output U2 is connected tothe CSN (current sense pin 2) input of regulator/LED driver U1.Regulator/LED driver U1 output DRV (pin 5) is routed to gate of Nchannel MOSFET Q1, the output of which feeds Schottky diode D8 toprovide a regulated input voltage VIN for the LEDs. While a standarddiode may be used for D8, a Schottky diode is preferred because of itslower forward voltage drop, i.e., approximately 0.25 V_(f) for theSchottky diode versus approximately 0.6 V_(f) for a standard diode.

The voltage drop at series connected resistors R1 and R2 providesregulated DC voltage to the plurality of LEDs, LED1, LED2, and LED3.Resistor R7 and capacitor C3 provide adequate isolation of VCC (pin 6)from ground (pin 4) on regulator/driver chip U1. Inductor L1 functionsin conjunction with filter capacitors C1-C2 to provide additional DCripple filtering. However, since L1 is disposed between LED3 and Q1, theinductance value may be reduced to approximately 50 μH, therebymaintaining a miniature form factor that is compatible with the MR-16lamp form factor.

Referring again to FIG. 4, it is shown that the present invention may bescaled up to accommodate an even greater plurality of LED lights, suchas the 10 LED array comprised of LED1′ through LED10′. As discussed indetail supra, transient limiting zener diodes U3′ and U4′ are disposedin parallel with ceramic power conditioning capacitor C13′. C13′, likeC5 of FIG. 3, provides a path for high frequency components of anelectronic switching power supply output at J1′ and J2′ so that theelectronic power supply senses an adequate load to energize itself. Toincrease the efficiency of the voltage rectification, Schottky diodesD1′, D2′, D3′, and D4′ having a low V_(f) (approximately 0.25 volts) areprovided.

Filter capacitors C1′ through C9′ are preferably tantalum and have aMean Time Between Failure (MTBF) of the same order of magnitude as MTBFfor a typical LED array, such as LED array LED1′ through LED10′. R1′ andR2′ perform the same function as R1 and R2 of FIG. 3. However, the LEDdriver circuitry U1′ is further protected from AC transient inputs bycapacitor C14′ in parallel with resistors R1′ and R2′.

Inputs 1′ through 6′ of LED driver circuitry U1′ are configuredsimilarly to the connections in FIG. 3. However, in addition to thermalrunaway protection as provided by shunt regulator U2′ and associatedresistor circuitry R4′, R5′ (thermistor), and R6′, the LED lampcircuitry as shown in FIG. 4 is protected from voltage runawayconditions via R7′ R8′, C10′ and transistor Q2′, the output of which isalso connected to dimmer input DIM (pin 3′). Q2′ has a pullup resistorR3′, while the VCC input of driver U1′ has a pullup resistor R10′. DCisolation from ground is provided by capacitor C12′.

Regulator/LED driver U1′ output DRV (pin 6′) is routed to gate of Nchannel MOSFET Q1′ the output of which feeds diode D5′ to provide aregulated input voltage VIN for the LED array LED1′-LED10′. C11′ isdisposed in parallel with the LED array and provides additional voltagesmoothing to counteract any voltage differences that may arise betweenthe two array arms LED1′-LED5′ and LED6′-LED10′. Inductor L1′ functionsin conjunction with C1′-C9′ to provide additional DC ripple filtering.However, since L1′ is disposed between R1′ and Q1′, the inductance valuemay be reduced to approximately 50 μH, thereby maintaining a miniatureform factor that is compatible with the MR-16 lamp form factor.

Referring to FIG. 5, the LED replacement for low voltage lamps mayinclude dimmer compensation circuitry formed by diode D13, resistor R13,and capacitor C4. This dimmer compensation circuitry allows forflicker-free dimming with the use of a low voltage electronic powersupply and an electronic low voltage dimmer. Trailing edge dimmers chopthe AC waveform at the beginning of the 60 Hz cycle, which does notsupply enough voltage at low dimming levels to keep the drive chip U1MAXI 6820 (or equal) alive or awake. This affects the output of the LEDsby abruptly reducing the current to the LEDs each time the drive chip“falls asleep”. This on-off cycling of the LED output becomes noticeableas a trembling and a flicker as the voltage to the chip is dimmed tobelow 8 VDC. The dimming compensation circuitry is connected to the CSNand DIM inputs of driver U1.

FIG. 5 is substantially identical to FIG. 3, except for the addition ofresistor R13 at pin 2 of the drive chip U1 and the addition of diode D13connected between capacitor C4 and the shunt regulator U2. The diodeD13, resistor R13 and capacitor C4 are an exemplary configurationconnected to drive chip U1 that accomplishes the required dimmercompensation to avoid lamp flicker during the dimming process. Thisdimmer compensation circuit allows the LED MR16 to dim flicker-free witha trailing edge dimmer by allowing the capacitor C4 to be continuallyfed current from the main branch after the ripple capacitors so thatcapacitor C4 receives 12 VDC continually and stores it. The capacitor C4delivers the current to the drive chip U1, ensuring that voltage neverdrops to a critical level even when dimming levels are extremely low.

Moreover, the diode D13 acts as a one-way valve and ensures that whenthe capacitor C4 is discharging, current does not feed back into themain circuit.

Additionally, the value of resistor R13 may be calculated to ensure thatthe capacitor C4 does not discharge too quickly, i.e., R13 and C4 forman R-C circuit in which the capacitor C4 retains sufficient remainingcharge to keep the chip U1 “awake” during the low voltage cycle.Moreover, the value of resistor R13 may be selected so that resistor R13protects the chip U1 from receiving excessive drive current.

It is to be understood that the present invention is not limited to theembodiments described above, but encompasses any and all embodimentswithin the scope of the following claims.

1. An LED replacement for low voltage lamps, comprising: a housing; aplurality of light emitting diodes disposed in the housing; atranslucent, reflective lens disposed on the housing, the translucent,reflective lens focusing light emissions from the light emitting diodesaway from the housing; lamp-energizing electrical contacts disposed atthe back of the housing; voltage rectification-voltage regulation LEDdriver circuitry, the voltage rectification-voltage regulation LEDdriver circuitry accepting as input a low voltage alternating currentfrom a transformer and producing a constant current regulated voltageresponsive thereto as output to the LEDs; a ceramic capacitorelectrically connected across the low voltage alternating current input,the ceramic capacitor providing an adequate load to the transformer tocause the transformer to energize the input; thermal protectioncircuitry connected to the voltage rectification-voltage regulation LEDdriver circuitry, the thermal protection circuitry throttling back powerto the light emitting diodes as the LED lamp exceeds a predeterminedthreshold temperature; a pair of zener diodes in parallel with theceramic capacitor at the low voltage alternating current input, thezener diodes having their respective anodes connected together and theirrespective cathodes connected to respective terminals of the low voltagealternating current input; and a dimmer compensation circuit connectedbetween the thermal protection circuitry and the voltagerectification-voltage regulation LED driver circuitry for providingsufficient voltage to the LED driver circuitry to maintain the lightemitting diodes flicker-free when the thermal protection circuitrythrottles back power to the light emitting diodes.
 2. The LEDreplacement according to claim 1, wherein the housing is compatible withan MR-16 form factor.
 3. The LED replacement according to claim 1,wherein the voltage rectification circuitry comprises a plurality ofdiodes in a full-wave rectification configuration.
 4. The LEDreplacement according to claim 1, further comprising a Schottky diodeelectrically disposed at the output of a voltage regulator/driverportion of the voltage rectification-voltage regulation LED drivercircuitry.
 5. The LED replacement according to claim 1, furthercomprising dimming compensation circuitry connected to a dimming inputof said rectification-voltage regulation LED driver circuitry.
 6. TheLED replacement according to claim 1, wherein the voltage rectificationportion of the LED driver circuitry further comprises a plurality oftantalum capacitors electrically disposed in parallel across therectifier output.
 7. The LED replacement according to claim 1, whereinthe thermal protection circuitry has a configuration for pulse widthmodulation dimming.
 8. The LED replacement according to claim 1, whereinthe thermal protection circuitry is configured for linear dimming. 9.The LED replacement according to claim 1, wherein the plurality of lightemitting diodes is electrically disposed in parallel rows, a smoothingcapacitor being disposed in parallel across the rows of LEDs.
 10. TheLED replacement according to claim 1, wherein the ceramic capacitor hasa value that is approximately 0.015 uF at approximately a 50-voltrating.
 11. The LED replacement according to claim 1, wherein the pairof zener diodes provides an approximately 19-volt clipping action. 12.An LED replacement for low voltage lamps, comprising: a housing; aplurality of light emitting diodes disposed in the housing; atranslucent, reflective lens disposed on the housing, the translucent,reflective lens focusing light emissions from the light emitting diodesaway from the housing; lamp-energizing electrical contacts disposed atthe back of the housing; voltage rectification-voltage regulation LEDdriver circuitry, the voltage rectification-voltage regulation LEDdriver circuitry accepting as input a low voltage alternating currentfrom a transformer producing a constant current regulated voltageresponsive thereto as output to the LEDs, wherein voltageregulator/driver portion of the voltage rectification-voltage regulationLED driver circuitry comprises approximately 2 MHz high-brightness LEDdrivers having high-side current sense and approximately 5000:1 dimming;a ceramic capacitor electrically connected across the low voltagealternating current input, the ceramic capacitor providing an adequateload to the transformer to cause the transformer to energize input;thermal protection circuitry connected to the voltagerectification-voltage regulation LED driver circuitry, the thermalprotection circuitry throttling back power to the light emitting diodesas the LED lamp exceeds a predetermined threshold temperature; and adimmer compensation circuit connected between the thermal protectioncircuitry and the voltage rectification-voltage regulation LED drivercircuitry for providing sufficient voltage to the LED driver circuitryto maintain the light emitting diodes flicker-free when the thermalprotection circuitry throttles back power to the light emitting diodes.13. An LED replacement for low voltage lamps, comprising: a housing; aplurality of light emitting diodes disposed in the housing; atranslucent, reflective lens disposed on the housing, the translucent,reflective lens focusing light emissions from the light emitting diodesaway from the housing; lamp-energizing electrical contacts disposed atthe back of the housing; voltage rectification-voltage regulation LEDdriver circuitry, the voltage rectification-voltage regulation LEDdriver circuitry accepting as input a low voltage alternating currentfrom a transformer and producing a constant current regulated voltageresponsive thereto as output to the LEDs; a ceramic capacitorelectrically connected across the low voltage alternating current input,the ceramic capacitor providing an adequate load to the transformer tocause the transformer to energize the input; thermal protectioncircuitry connected to the voltage rectification-voltage regulation LEDdriver circuitry, the thermal protection circuitry throttling back powerto the light emitting diodes as the LED lamp exceeds a predeterminedthreshold temperature, wherein the thermal protection circuitry has aconfiguration that initiates power throttleback at approximately 60° C.,the configuration being characterized by a throttling back gradientcutting the power by 50% at approximately 85% of the maximum allowabletemperature; and a dimmer compensation circuit connected between thethermal protection circuitry and the voltage rectification-voltageregulation LED driver circuitry for providing sufficient voltage to theLED driver circuitry to maintain the light emitting diodes flicker-freewhen the thermal protection circuitry throttles back power to the lightemitting diodes.